/* ==========================================
 * JGraphT : a free Java graph-theory library
 * ==========================================
 *
 * Project Info:  http://jgrapht.sourceforge.net/
 * Project Creator:  Barak Naveh (http://sourceforge.net/users/barak_naveh)
 *
 * (C) Copyright 2003-2006, by Barak Naveh and Contributors.
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; if not, write to the Free Software Foundation,
 * Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
 */
/* -------------------
 * WheelGraphGenerator.java
 * -------------------
 * (C) Copyright 2003-2006, by John V. Sichi and Contributors.
 *
 * Original Author:  John V. Sichi
 * Contributor(s):   -
 *
 * $Id: WheelGraphGenerator.java,v 1.2 2007/05/22 15:52:53 kjellw Exp $
 *
 * Changes
 * -------
 * 16-Sep-2003 : Initial revision (JVS);
 *
 */
package org.jgrapht.generate;

import java.util.*;

import org.jgrapht.*;

/**
 * Generates a <a href="http://mathworld.wolfram.com/WheelGraph.html">wheel
 * graph</a> of any size. Reminding a bicycle wheel, a wheel graph has a hub
 * vertex in the center and a rim of vertices around it that are connected to
 * each other (as a ring). The rim vertices are also connected to the hub with
 * edges that are called "spokes".
 * 
 * @author John V. Sichi
 * @since Sep 16, 2003
 */
public class WheelGraphGenerator<V, E> implements GraphGenerator<V, E, V> {
	// ~ Static fields/initializers
	// ---------------------------------------------

	/**
	 * Role for the hub vertex.
	 */
	public static final String HUB_VERTEX = "Hub Vertex";

	// ~ Instance fields
	// --------------------------------------------------------

	private boolean inwardSpokes;

	private int size;

	// ~ Constructors
	// -----------------------------------------------------------

	/**
	 * Creates a new WheelGraphGenerator object. This constructor is more
	 * suitable for undirected graphs, where spokes' direction is meaningless.
	 * In the directed case, spokes will be oriented from rim to hub.
	 * 
	 * @param size
	 *            number of vertices to be generated.
	 */
	public WheelGraphGenerator(int size) {
		this(size, true);
	}

	/**
	 * Construct a new WheelGraphGenerator.
	 * 
	 * @param size
	 *            number of vertices to be generated.
	 * @param inwardSpokes
	 *            if <code>true</code> and graph is directed, spokes are
	 *            oriented from rim to hub; else from hub to rim.
	 * 
	 * @throws IllegalArgumentException
	 */
	public WheelGraphGenerator(int size, boolean inwardSpokes) {
		if (size < 0) {
			throw new IllegalArgumentException("must be non-negative");
		}

		this.size = size;
		this.inwardSpokes = inwardSpokes;
	}

	// ~ Methods
	// ----------------------------------------------------------------

	/**
	 * {@inheritDoc}
	 */
	public void generateGraph(Graph<V, E> target,
			final VertexFactory<V> vertexFactory, Map<String, V> resultMap) {
		if (size < 1) {
			return;
		}

		// A little trickery to intercept the rim generation. This is
		// necessary since target may be initially non-empty, meaning we can't
		// rely on its vertex set after the rim is generated.
		final Collection<V> rim = new ArrayList<V>();
		VertexFactory<V> rimVertexFactory = new VertexFactory<V>() {
			public V createVertex() {
				V vertex = vertexFactory.createVertex();
				rim.add(vertex);

				return vertex;
			}
		};

		RingGraphGenerator<V, E> ringGenerator = new RingGraphGenerator<V, E>(
				size - 1);
		ringGenerator.generateGraph(target, rimVertexFactory, resultMap);

		V hubVertex = vertexFactory.createVertex();
		target.addVertex(hubVertex);

		if (resultMap != null) {
			resultMap.put(HUB_VERTEX, hubVertex);
		}

		for (V rimVertex : rim) {
			if (inwardSpokes) {
				target.addEdge(rimVertex, hubVertex);
			} else {
				target.addEdge(hubVertex, rimVertex);
			}
		}
	}
}

// End WheelGraphGenerator.java
